Data Sources

At AvnWx.com, we're pilots, too. We strive for accurate, real-time data, because no one cares about yesterday's weather. Also, because we'd rather be flying we don't want to have hard-coded data which forces us to manually update this site to keep it accurate.

However, you agree to use this website for information only. You must contact an official Weather Briefer prior to flight to make sure you have the latest weather and NOTAMs. AvnWx.com cannot guarantee fully accurate delivery of complete briefing information.

	Source	AvnWx.com Coverage	Update Frequency of Source	Update Frequency of AvnWx.com
METAR	NOAA/ADDS	World-wide, Military bases included	Hourly, but can be revised anytime. Warning symbol, is displayed with details, if station's data more than 90 minutes old.	5 minutes
PIREP	NOAA/ADDS	World-wide	When reported by pilots Typically, AFSS will report PIREPs typically no older than 1.5 hours	5 minutes AvnWx will show PIREPs up to 5 hours old, based on your set preference
TAF	NOAA/ADDS	World-wide, Military bases included	Typically issued for 24-hour period, four times daily, updated as required. Warning symbol, is displayed with details, if station's data more than 12 hours old.	10 minutes
AIRMET	NOAA/ADDS	US only	Issued every 6 hours, covers 6 hour forecast period, updated as required	10 minutes
SIGMET	NOAA/ADDS	US only	Unscheduled, updated as required	10 minutes
Winds Aloft	NOAA	CONUS and Alaska	Issued every 6 hours	30 minutes
TFR	FAA	US	Unscheduled. If the FAA reporting site is down, AvnWx.com shows most recent data and displays warning symbol in the menu, next to TFR selection.	15 minutes
Stadium TFR	FAA (TFR) Major League Baseball (Schedule) National Football League (Schedule) Major Motor Speedway races NCAA Football (Schedule)	US and Canada	N/A	nightly, but note that events may be delayed hours or days without notice.
NEXRAD Precipitation Radar	IEM	CONUS	Approx. 5 minutes	5 minutes. Animation supports previous 45 minutes, in 5 minute increments
Airport Facilities Directory	FAA	US	56 days	nightly, just to make sure nothing sneaks by.
Procedures	FAA	US	28 days	nightly
Airport/Navaid/Reporting Fix Details	NFDC	US	56 days	56 days
Airspace Boundaries	NFDC	US	56 days	56 days
Surface Analysis	NOAA HPC	North America	Updated every three hours	15 minutes

METARs, PIREPs, TAFs, Inflight Weather Advisories (SIGMETs, AIRMETs)

These are obtained directly from the Aviation Digital Data Server (ADDS), part of the NOAA's National Weather Service. This data (i.e., the raw METARs, PIREPs, advisories and TAFs) is not subject to copyright protection. The presentation and translation of the raw data is provided and copyrighted by AvnWx.com. Because of the experimental nature of the ADDS service, AvnWx.com cannot full-time guarantee access to the information, and should not be relied upon in lieu of officially disseminated weather forecasts and warnings.

AvnWx.com obtains updates every few minutes. You can see the time of the most recent update in menu, next to the particular weather item. At time of the update, we have the most recently available data. You're seeing the most recent information available from ADDS.

Winds and Temperatures Aloft

Winds and Temperatures Aloft forecasts are obtained from NOAA's Aviation Weather website.

The website is polled once per hour to make sure we have the latest. See also AvnWx.com -- About Forecast Winds and Temps Aloft

Temporary Flight Restrictions

Temporary Flight Restrictions are obtained directly from FAA's Graphic TFR webpage. The website is polled every 15 minutes to make sure we have the latest set of current TFRs. Details for these TFRs are then downloaded, manipulated and stored locally. See also AvnWx.com -- About Temporary Flight Restrictions

Special handling is performed for the Stadium TFR. Using published schedules for Major League Baseball and National Football League AvnWx.com displays TFR areas for upcoming games. Note that the TFR applies to "one hour before to one hour after" the game. Games are estimated to last three hours, but AvnWx.com has no way of determining the precise end of a game. Major Motor Speedway events are handled in a similar manner.

Airport/Facilities Directory

The pages displayed by AvnWx.com for the A/FD are obtained directly from the FAA. Since these are updated every 56 days, AvnWx.com gets the update also. You can check the the currency of the entry by looking at the date on the bottom of each page of the A/FD. A/FD often have runway diagrams for smaller airports, so if you don't see a full airport diagram for an airport, check its entry in the A/FD.

Procedures

Arrival, Approach, and Departure procedures are obtained directly from the FAA. FAA issues new versions every 28 days, even though the procedure itself may not have changed. Always note the date on the side of the printed procedure plate. These pages are available only from the airport's detailed page. (Right-click on a METAR symbol or Airport symbol and select Airport details..., or browse airports at maps.AvnWx.com/airport, for example maps.AvnWx.com/airport/KORD)

Surface Analysis Overlay

Surface Analysis overlay, showing warm and cold fronts, is drawn from data provided by NOAA's HPC. New data is provided approximately every three hours. AvnWx.com checks for new data every fifteen minutes, and will draw a new frontal system when new data is obtained. See AvnWx.com -- About Surface Analysis for more information.

NEXRAD Precipitation Overlay

This overlay is the NEXRAD Base Reflectivity, provided by IEM. The data is gathered by IEM and regenerated every 5 minutes. Though it is updated every 5 minutes, the base radar images are not all updated every five minutes and therefore the resulting composite may not be fully updated every 5 minutes. Use this image as merely a guide current precipitation. Turning on animation menu, will show the previous 45 minutes of radar images, pausing a few seconds at the most recent image. This is useful to see direction of weather and trends. It also helps when there appears to be a missing radar echo. Note that echos change rapidly, so use echos for general planning only. Avoid thunderstorms by at least 20 miles, and recall that cumulonimbus can grow in less than one hour.

Turning on NEXRAD will overload computers with 512M or less RAM, or computers on slow links -- you've been warned!

Other

We use tables and additional algorithms for all sorts of other useful information.

Sunrise/Sunset, Lunar Phase tables
This is calculated algorithmically, based on the location's latitude longitude, using algorithms from NOAA and Keith Peter Burnett (bodmas.org/astronomy/riset.html)
Magnetic deviation calculation
With each airport, the FAA publishes a magnetic deviation, with a date that value was made. This information is visible on the detailed page for each airport. Magnetic deviation shifts over the years, and the FAA doesn't get around to updating the magnetic variations too often for the smaller airports. For this reason, AvnWx.com provides both the FAA's value, as well as a newly calculated value, based on World Magnetic Model (WMM-2005) from NGDC. These values rarely differ by more than a few degrees, but you should be aware of that your GPS or magnetic compass will disagree with the field alignment. Winds are published as True, runway heading were (mostly) magnetic when built, but may be 10+ degrees off as magnetic north has shifted. This also means that a VOR bearing may not match magnetic bearing. When AvnWx.com displays flight path information, the reported magnetic heading is based on "real"/"current" magnetic heading, which may be different than the VOR heading you need to fly.
Density Altitude Calculation
Density altitude is shown with METAR information, when we have sufficient current information. To calculate accurately, we need station elevation, current temperature, current dewpoint, and current barometric pressure. When the METAR does not report all information, we will not show density altitude. Details on density altitude are from Richard Shelquist's excellent set of calculators at wahiduddin.net/calc.
Flight Path Calculation
Flight paths are calculated along a great circle route. We're indebted to Ed Williams (williams.best.vwh.net) for providing great algorithms useful for performating these calculations.

Suggestions? Questions? Corrections? Let us know! Email